Electrically conductive adhesive

Abstract

An electrically conductive adhesive layer is described. The adhesive layer includes an adhesive material and pluralities of electrically conductive at least first and second particles. The adhesive layer may have a thickness less than about 35 micrometers and an electrical resistance in the thickness direction of less than about 30 milliohms. A total volume of the pluralities of particles may be greater than 40% of a total volume of the adhesive layer. The first and second particles may have different shapes.

What is claimed is: 
     
       1. An electrically conductive adhesive layer having an average thickness of less than about 15 micrometers and an electrical resistance in a thickness direction of less than about 30 milliohms, the adhesive layer comprising:
 an adhesive material; 
 pluralities of electrically conductive at least first and second particles, each first particle having a length L 1 , a width W 1 , and a thickness H 1 , L 1  and W 1  each greater than about 5 H 1  for at least a majority of the first particles, the first particles comprising silver-coated copper particles, the silver-coated copper particles comprising silver coatings comprising outermost major surfaces of the silver-coated copper particles and forming interfaces with copper cores of the silver-coated copper particles, 
 a ratio of a total volume of the pluralities of the at least first and second particles to a total volume of the adhesive layer greater than about 40%, the at least first and second particles dispersed uniformly in the adhesive material such that for a majority of the first particles, the thickness direction of each first particle is substantially parallel to the thickness direction of the adhesive layer, and for a majority of the second particles, a maximum dimension of each second particle in the thickness direction of the adhesive layer is greater than about 5 H 1 . 
 
     
     
       2. The electrically conductive adhesive layer of  claim 1 , wherein the pluralities of electrically conductive at least first and second particles comprises a plurality of third particles, each third particle different from the first and second particles. 
     
     
       3. The electrically conductive adhesive layer of  claim 1  being more electrically conductive in the thickness direction and less electrically conductive in an in-plane direction. 
     
     
       4. The electrically conductive adhesive layer of  claim 1 , wherein L 1  and W 1  are each greater than about 5 H 1  for at least 75% of the first particles. 
     
     
       5. The electrically conductive adhesive layer of  claim 1 , wherein for at least 75% of the first particles, the thickness direction of each first particle is substantially parallel to the thickness direction of the adhesive layer. 
     
     
       6. The electrically conductive adhesive layer of  claim 1 , wherein for a majority of the second particles, the maximum dimension of each second particle in the thickness direction of the adhesive layer is greater than about 10 H 1 . 
     
     
       7. The electrically conductive adhesive layer of  claim 1 , wherein each second particle has a length L 2 , a width W 2 , and a thickness H 2 , L 2 /H 2 , W 2 /H 2  and L 2 /W 2  each in a range from about 0.1 to about 10 for at least a majority of the second particles. 
     
     
       8. The electrically conductive adhesive layer of  claim 1 , wherein for at least a majority of the first particles, each first particle is flake like or plate like. 
     
     
       9. The electrically conductive adhesive layer of  claim 1 , wherein for at least a majority of the second particles, each second particle is a dendritic particle. 
     
     
       10. The electrically conductive adhesive layer of  claim 1 , wherein the first particles are substantially two-dimensional particles and the second particles are substantially three-dimensional particles. 
     
     
       11. The electrically conductive adhesive layer of  claim 1 , wherein a ratio of a total weight of the first particles to a total weight of the second particles is in a range from about 0.1 to about 10. 
     
     
       12. The electrically conductive adhesive layer of  claim 1  having a peel strength of at least 0.1 N/mm from a stainless steel surface after a dwell time of about 20 minutes at 22° C. 
     
     
       13. The electrically conductive adhesive layer of  claim 1 , wherein the adhesive material comprises one or more of a pressure sensitive adhesive, a hot melt adhesive, a thermoset adhesive, a thermoplastic adhesive, a UV adhesive, a liquid adhesive, a solvent based adhesive, and a water based adhesive. 
     
     
       14. The electrically conductive adhesive layer of  claim 1 , wherein the first particles have a cumulative 50% particle diameter D50 in a range from about 5 micrometers to about 50 micrometers. 
     
     
       15. The electrically conductive adhesive layer of  claim 1 , wherein the second particles have a cumulative 50% particle diameter D50 in a range from about 5 micrometers to about 50 micrometers. 
     
     
       16. An adhesive transfer tape comprising:
 the electrically conductive adhesive layer of  claim 1 ; and 
 a first release liner releasably attached to a first major surface of the adhesive layer.